1. Field of the Invention
The present invention relates to a travel device and a control method of the same and, particularly, to a travel device that performs drive control based on its own detected attitude information and a control method of the same.
2. Description of Related Art
Travel devices for traveling with a person on board with various body constructions and vehicle structures are proposed that detect their own attitude information and performs drive control based on the detected attitude information. Such travel devices make motion according to the attitude control principle based on an inverted pendulum and, specifically, detect their own attitude information by using a gyroscope and an acceleration sensor incorporated therein, compute a rotation command to a motor so as to maintain the attitude and transmit rotation command data to a motor control device. The travel devices can travel according to a change in the center of gravity and posture of a person on board while maintaining their attitude based on such feedback control.
For example, Japanese Unexamined Patent Publications Nos. 2006-211899 and 2006-315666 disclose a coaxial two-wheel vehicle in which two wheels are mounted coaxially. Such a coaxial two-wheel vehicle is structurally unstable fore and aft and therefore stabilizes the attitude by controlling the wheels based on feedback from an attitude sensor. Further, in the coaxial two-wheel vehicle, the operation of the vehicle such as forward and backward movement and left and right turns is performed in response to a command according to the shift of a rider's center of gravity, a command according to the tilt of a step, a command from a control stick or the like. Alternatively, remote control operation by external command input or automatic movement based on trajectory planning may be performed in some cases.
However, in a control system of the coaxial two-wheel vehicle related to the present invention, there is a concern that adjustment of control parameters in an attitude controller is extremely difficult, thus requiring lots of work and time for the adjustment. Further, there is a concern that robustness against rider's weight variation or the like is low.
The concerns of the coaxial two-wheel vehicle related to the present invention are described hereinafter in further detail. In the related coaxial two-wheel vehicle, a control system that generates a torque command and inputs it to a motor amplifier is typically used in the case of making control of at least one of a vehicle pitch angle and pitch angular velocity only, or, making both control of at least one of a vehicle pitch angle and pitch angular velocity and control of at least one of a vehicle position, velocity, directional angle (yaw direction) and directional velocity (yaw velocity) simultaneously.
FIG. 15 is a control block diagram showing a control system shown in FIG. 33 of Japanese Unexamined Patent Publication No. 2006-211899. In the control system shown in FIG. 15, K1 and K2 are used as control parameters related to control of the vehicle pitch angle and pitch angular velocity, and K3 and K4 are used as control parameters related to control of the vehicle position and velocity. It is thus necessary in the control system shown in FIG. 15 to adjust the control parameters K1 to K4 in such a way that control of the vehicle pitch angle and pitch angular velocity and control of the vehicle position and velocity are implemented simultaneously.
Because the coaxial two-wheel vehicle is the inverted pendulum, there is a physical constraint that it is always necessary to tilt a vehicle pitch angle when performing control action such as acceleration or deceleration. For example, in the case of decelerating and then halting the coaxial two-wheel vehicle, if the vehicle is controlled to decelerate simply, the coaxial two-wheel vehicle fails to maintain the inverted position due to the inertia and thus falls down frontward. Therefore, in the case of decelerating and then halting the coaxial two-wheel vehicle, it is necessary to control the vehicle so as to accelerate forward in the traveling direction once, so that the vehicle comes ahead of a rider (i.e., it is necessary to change the vehicle pitch angle in such a way that the upper body of the rider is bent backward). After the upper body of the rider is bent backward, the vehicle velocity is reduced gradually so that it halts with the inverted position maintained at the time when the vehicle velocity reaches zero, thereby avoiding falling down of the vehicle during deceleration. Accordingly, during acceleration or deceleration action, it is incapable of controlling the vehicle pitch angle and the vehicle position independently of each other, such as changing the vehicle position with the vehicle pitch angle maintained horizontally or making the vehicle stand still at a given position with the vehicle pitch angle tilting. Hence, the control parameters (K1 and K2 in FIG. 15) related to the vehicle pitch attitude (pitch angle and pitch angular velocity) and the control parameters (K3 and K4 in FIG. 15) related to the vehicle position and velocity are closely correlated with each other and cannot be determined independently of each other.
If accurate modeling of a control target is possible, a relationship between control parameters can be mathematically determined by using the optimal regulator technique or the like. However, adjustment of control parameters is generally difficult due to friction, disturbance, error and so on, which cannot be modeled. Particularly, adjustment of control parameters is extremely difficult due to error of the mass and the moment of inertia or the like caused by varying height and weight of riders.
As described above, in the control system of the related coaxial two-wheel vehicle, there is a concern that adjustment of control parameters in the attitude controller is extremely difficult, and lots of work and time are required for the adjustment. Further, there is a concern that robustness against rider's weight variation or the like is low.
In light of the above concerns, it is desirable to provide a travel device that enables easy implementation of a control system capable of performing quick and easy adjustment of control parameters and further having high robustness, and a control method of the same.